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- <meta name="AUTHOR" content="pme@gcc.gnu.org (Phil Edwards)" />
- <meta name="KEYWORDS" content="HOWTO, libstdc++, GCC, g++, libg++, STL" />
- <meta name="DESCRIPTION" content="HOWTO for the libstdc++ chapter 26." />
- <meta name="GENERATOR" content="vi and eight fingers" />
- <title>libstdc++-v3 HOWTO: Chapter 26</title>
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-
-<h1 class="centered"><a name="top">Chapter 26: Numerics</a></h1>
-
-<p>Chapter 26 deals with building block abstractions to aid in
- numerical computing:
-</p>
-<ul>
- <li>Template data structures such as <code>valarray<></code>
- and <code>complex<></code>.
- </li>
- <li>Template numerical functions such as <code>accumulate</code>,
- <code>inner_product</code>, <code>partial_sum</code>, and
- <code>adjacent_difference</code>.
- </li>
-</ul>
-<p>All of the Standard C math functions are of course included in C++,
- and overloaded versions for <code>long</code>, <code>float</code>, and
- <code>long double</code> have been added for all of them.
-</p>
-
-<!-- ####################################################### -->
-<hr />
-<h1>Contents</h1>
-<ul>
- <li><a href="#1">Complex Number Processing</a></li>
- <li><a href="#2">Array Processing</a></li>
- <li><a href="#3">Numerical Functions</a></li>
- <li><a href="#4">C99</a></li>
-</ul>
-
-<hr />
-
-<!-- ####################################################### -->
-
-<h2><a name="1">Complex Number Processing</a></h2>
- <p>Using <code>complex<></code> becomes even more comple- er, sorry,
- <em>complicated</em>, with the not-quite-gratuitously-incompatible
- addition of complex types to the C language. David Tribble has
- compiled a list of C++98 and C99 conflict points; his description of
- C's new type versus those of C++ and how to get them playing together
- nicely is
-<a href="http://david.tribble.com/text/cdiffs.htm#C99-complex">here</a>.
- </p>
- <p><code>complex<></code> is intended to be instantiated with a
- floating-point type. As long as you meet that and some other basic
- requirements, then the resulting instantiation has all of the usual
- math operators defined, as well as definitions of <code>op<<</code>
- and <code>op>></code> that work with iostreams: <code>op<<</code>
- prints <code>(u,v)</code> and <code>op>></code> can read <code>u</code>,
- <code>(u)</code>, and <code>(u,v)</code>.
- </p>
- <p>Return <a href="#top">to top of page</a> or
- <a href="../faq/index.html">to the FAQ</a>.
- </p>
-
-<hr />
-<h2><a name="2">Array Processing</a></h2>
- <p>One of the major reasons why FORTRAN can chew through numbers so well
- is that it is defined to be free of pointer aliasing, an assumption
- that C89 is not allowed to make, and neither is C++98. C99 adds a new
- keyword, <code>restrict</code>, to apply to individual pointers. The
- C++ solution is contained in the library rather than the language
- (although many vendors can be expected to add this to their compilers
- as an extension).
- </p>
- <p>That library solution is a set of two classes, five template classes,
- and "a whole bunch" of functions. The classes are required
- to be free of pointer aliasing, so compilers can optimize the
- daylights out of them the same way that they have been for FORTRAN.
- They are collectively called <code>valarray</code>, although strictly
- speaking this is only one of the five template classes, and they are
- designed to be familiar to people who have worked with the BLAS
- libraries before.
- </p>
- <p>Some more stuff should go here once somebody has time to write it.
- </p>
- <p>Return <a href="#top">to top of page</a> or
- <a href="../faq/index.html">to the FAQ</a>.
- </p>
-
-<hr />
-<h2><a name="3">Numerical Functions</a></h2>
- <p>There are four generalized functions in the <numeric> header
- that follow the same conventions as those in <algorithm>. Each
- of them is overloaded: one signature for common default operations,
- and a second for fully general operations. Their names are
- self-explanatory to anyone who works with numerics on a regular basis:
- </p>
- <ul>
- <li><code>accumulate</code></li>
- <li><code>inner_product</code></li>
- <li><code>partial_sum</code></li>
- <li><code>adjacent_difference</code></li>
- </ul>
- <p>Here is a simple example of the two forms of <code>accumulate</code>.
- </p>
- <pre>
- int ar[50];
- int someval = somefunction();
-
- // ...initialize members of ar to something...
-
- int sum = std::accumulate(ar,ar+50,0);
- int sum_stuff = std::accumulate(ar,ar+50,someval);
- int product = std::accumulate(ar,ar+50,1,std::multiplies<int>());
- </pre>
- <p>The first call adds all the members of the array, using zero as an
- initial value for <code>sum</code>. The second does the same, but uses
- <code>someval</code> as the starting value (thus, <code>sum_stuff == sum +
- someval</code>). The final call uses the second of the two signatures,
- and multiplies all the members of the array; here we must obviously
- use 1 as a starting value instead of 0.
- </p>
- <p>The other three functions have similar dual-signature forms.
- </p>
- <p>Return <a href="#top">to top of page</a> or
- <a href="../faq/index.html">to the FAQ</a>.
- </p>
-
-<hr />
-<h2><a name="4">C99</a></h2>
- <p>In addition to the other topics on this page, we'll note here some
- of the C99 features that appear in libstdc++-v3.
- </p>
- <p>The C99 features depend on the <code>--enable-c99</code> configure flag.
- This flag is already on by default, but it can be disabled by the
- user. Also, the configuration machinery will disable it if the
- necessary support for C99 (e.g., header files) cannot be found.
- </p>
- <p>As of GCC 3.0, C99 support includes classification functions
- such as <code>isnormal</code>, <code>isgreater</code>,
- <code>isnan</code>, etc.
- The functions used for 'long long' support such as <code>strtoll</code>
- are supported, as is the <code>lldiv_t</code> typedef. Also supported
- are the wide character functions using 'long long', like
- <code>wcstoll</code>.
- </p>
- <p>Return <a href="#top">to top of page</a> or
- <a href="../faq/index.html">to the FAQ</a>.
- </p>
-
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-See <a href="../17_intro/license.html">license.html</a> for copying conditions.
-Comments and suggestions are welcome, and may be sent to
-<a href="mailto:libstdc++@gcc.gnu.org">the libstdc++ mailing list</a>.
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